Limit switch operator

ABSTRACT

An apparatus for operating a rotating cam limit switch. The switch is fastened to the framework of a tilting electric arc furnace. The apparatus is a limit switch operator consisting of a pendulum suspended from a horizontal shaft and a pair of bevel gears. The bevel gears are mounted in meshing engagement on the limit switch shaft and the horizontal shaft respectively. As the furnace tilts, the limit switch moves in an arc around the pendulum. The pendulum remains vertical and provides the torque to the bevel gears that is required for initiating the limit switch contacts.

United States Patent Yohe et al.

[54] LIMIT SWITCH OPERATOR [72] Inventors: Robert A. Yohe, Steelton; George L. Mc-

Call, Harrisburg, both of Pa.

[73] Assignee: Bethlehem Steel Corporation [22] Filed: Nov. 23, 1970 [21] Appl. No.: 91,722

[52] US. Cl. ..200/61.48, 200/6139, 263/33 R [51] Int. Cl. ..H0lh 3/16 [58] Field of Search ..200/61.48, 6139,18, 85 R,

' ZOO/61.5, 61.52

[56] References Cited UNITED STATES PATENTS 2,151,439 3/1939 Pittman ..263/33 1 Jan. 18, 1972 2,677,021 4/1954 Baumgardner ..200/61.39 X

Primary Examiner-Robert K. Schaefer Assistant Examiner-M. Ginsburg Attorney-Joseph .l. O'Keefe [57] ABSTRACT An apparatus for operating a rotating cam limit switch. The switch is fastened to the framework of a tilting electric arc furnace. The apparatus is a limit switch operator consisting of a pendulum suspended from a horizontal shaft and a pair of bevel gears. The bevel gears are mounted in meshing engagement on the limit switch shaft and the horizontal shaft respectively. As the furnace tilts, the limit switch moves in an arc around the pendulum. The pendulum remains vertical and provides the torque to the bevel gears that is required for initiating the limit switch contacts.

5 Claims, 4 Drawing Figures PATENTEUJAMBIQYZ 316362843.

sum 1 or 2 0 Hg ANG/{E a 0 I (9 PE/VDULUM INVENTORS Robe/f A. 70/26 George L. Mc CaI/ PATENTEU JAN 1 8 I972 SHEET 2 [IF 2 INVENTORS Roberf A. Yohe GeorgeL. Me Call BY I 84 a! ATTORNEY LIMIT SWITCH OPERATOR BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an apparatus for operating a rotating cam limit switch. The switch is fastened to the framework of a tilting electric arc furnace. The furnace and the'switch travel through the same angle of rock. As the switch passes through this angle of rock the apparatus activates various calibrated cams contained within the limit switch.

2. Description of the Prior Art A characteristic of electric arc melting furnaces is the ability to oscillate or tilt. During the melting cycle the furnace oscillates or tilts toward the tap side or slag side. The major components of a tilting electric arc furnace are: the furnace shell, pouring spout, furnace doors, tilting mechanism, rockers and rails, electrodes and associated electrical equipment. The prior art specifically considered by the inventors concerns the tilting mechanism, rockers and rails.

The most commonly accepted tilting mechanism is a pair of hydraulic cylinders mounted vertically on the floor below the furnace. The cylinders are located on either side of the furnace working door and are fastened to the bottom of the furnace shell. Hydraulic tilting has found wide acceptance because it affords a very smooth tilt, both forward and backward. Tilt speeds vary from less than 5% to 1 per second assuming a maximum tilting angle at pour of 45 and a maximum backward tilting angle at slagging off of Movement of the piston within the hydraulic cylinder actually tilts the furnace. The furnace moves through the combination of a pair of toothed rockers riding on a pair of toothed rails. The rails are mounted on the furnace foundation piers and can be either curved or flat depending upon the furnace size and design. The rockers are attached to the furnace shell. The rocker curvature is designed to result in the furnace tilting forward to pour to a specified angle of tilt (usually 40 to 45) and having a backward tilt from horizontal of from 5 to l5 for slagging off.

At the conclusion of the refining period the refined melt is tapped by tilting the furnace toward the tap side. The melt discharges from the pouring spout into an awaiting ladle. The tile angle is gradually increased until the entire melt is tapped. At the end of the tap, slag is removed by tilting the furnace back and allowing the slag to run over the front door sill.

As the furnace oscillates through its rocking angle, toward the tap side or slag side, various functions must be activated or events recorded. In the prior art, these functions or events were activated or recorded by a series of limit switches and associated tripping member or operators.

These limit switches and their operators were located on or activated by the fumace proper. A first limit switch that was calibrated to open a power circuit when the furnace tilted 5 toward the slag side or 10 toward the tap side was located at the base of one of the furnace tilt cylinder well walls. The

function of this switch was to cut the furnace power off when one of these angles was exceeded. The contacts of this switch remained closed while the furnace was in normal level operation.

The first limit switch operator was a 4foot flat bar that was fastened to the bottom of the tilt cylinder. When the furnace was level the operator therefor would be parallel to the longitudinal axis of the limit switch. The operator would keep the switch activatedwhen the furnace was level. If the 5 or 10 angles were exceeded the operator would disengage the limit switch and the limit switch contacts would open. The length of the operator was dependent upon the distance the tilt cylinder piston would travel for a 5 or 10 movement.

A second limit switch, the furnace level limit switch, was also located at the base of a furnace tilt cylinder well wall. The function of this limit switch was to inform the furnace operator when the furnace was level. To charge the furnace, a ram is used to raise the furnace superstructure and top. During the refining period the furnace tends to oscillate slightly and the operator was a steel angle or the like welded to the bottom of r the tilt cylinder.

A third limit switch was the 40 toward tap limit switch. This switch was located at the top of the cylinder well wall. This limit switch performed two functions, it cut off the flow of hydraulic fluid thereby stopping movement of the tilt cylinder and also it transmitted a signal to the furnace computer. This signal printed out the tap time on a furnace heat log. The instant limit switch operator was likewise a steel angle fastened to the bottom of the tilt cylinder. When the tilt cylinder was fully extended the operator would actuate the limit switch.

A forth limit switch was the 5 toward slag limit switch. The switch was located on the furnace rocker rail. The function of this limit switch was to transmit a signal to the furnace computer that the furnace had slagged off. This signal printed out the slag off time on the furnace heat log. The limit switch operator was a steel angle fastened to the furnace rocker.

The problem associated with the prior art limit switches and operators was one of location. The switches and operators were all located below the furnace proper. As a matter of fact, with the exception of the switch located on the furnace rocker all the switches were located at the base of the tilt cylinder well wall, approximately 20 feet below ground level. The operators were located in equally inaccessible positions on the tilt cylinder. This inaccessibility presented a serious maintenance problem. If one of the switches malfunctioned during the refining period it was virtually impossible due to the elevated temperature around the furnace to repair the switch. Even normal maintenance when the furnace was shut down for repairs or relining was a difi'rcult procedure.

The inventors have developed a new limit switch operator. The individual functions of the several limit switches are incorporated into one multiple rotating cam limit switch. This switch is fastened to the framework of the furnace, above floor level, in an accessible area. This newly located switch has been calibrated to perform functions heretofore not available. The limit switch actuator of this invention is also accessible and capable of activating this limit switch.

SUMMARY OF THE INVENTION An object of the instant invention is to provide a limit switch operator that can be positioned in an accessible location.

A further object of this invention is to provide a limit switch operator that is sturdy and capable of withstanding severe service conditions.

Still a further object of this invention is to provide a single limit switch operator that will activate a plurality of electrical contacts thereby initiating several events from one limit switch.

These and other objects are achieved by replacing the several inaccessible limit switches with a rotating cam limit switch containing a plurality of cams and electrical contacts. The contacts are initiated during angular travel of the furnace by a single operator. The operator comprises a pendulum suspended from a horizontal shaft and a pair of bevel gears. The bevel gears are mounted in meshing engagement on the limit switch shaft and the horizontal shaft respectively. As the furnace tilts, the limit switch moves in an are around the pendulum. The pendulum remains vertical and provides the torque to the bevel gears that is required for initiating the individual contacts within the limit switch.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a graphic representation showing the oscillation of a tilting furnace toward the slag side and tapside.

FIG. 2 is a side view of the limit switch operator.

FIG. 3 is a sectional view taken through line 33 showing the limit switch fastened to the furnace framework and parallel to the centerline of the furnace.

FIG. 4 is a side view of the limit switch fastened to the furnace showing the furnace and switch tilting and the operator remaining vertical.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows the oscillation of a tilting furnace toward the tap side and the slag side. The centerline O- of the furnace (not shown) coincides with the centerline of the limit switch operator. Various functions that occur either on the tap side or slag side are represented by the letters a, b, c, d, e, f, and g. These functions correspond to specific angles of rock that will be hereinafter developed.

Shown in FIG. 2 is a rotating cam limit switch I mounted on platform 2 by fasteners 3. Platform 2 is fastened to the framework 4 of a tilting electric arc furnace (not shown).

Limit switch 1 contains a plurality of cams and cam operated contacts (not shown). The cams are mounted on rotating shaft 5 which extends beyond limit switch protective cover 6. Fastened to shaft 5 by means of keyway 7 and key 8 is small bevel gear 9.

Mounted on platform 2 are pillow blocks 10 and 11 which contain bores 12 and 13 respectively. Passing through said bores is horizontal shaft 14. Fastened to shaft 14 is a large bevel gear 15, which is secured on horizontal shaft 14 by keyway 16 and key 17. Said large bevel gear is in meshing engagement with small bevel gear 9.

Connected to shaft 14 between pillow blocks 10 and 11 is pendulum operator l8. Said operator 18 comprises weight 19 with central bore 20. Passing through bore 20 is shaft 21 containing threaded end 22.

The pendulum operator 18 is connected to horizontal shaft 14 by joining unthreaded end 23 to short round bar 24 containing central bore 25. Round bar 24 is fastened intermediate pillow blocks 10 and 11 by keyway 26, key 27 and setscrew 28. Operator shaft 21 is passed through weight bore 20 and nut 29 is threadably connected to threaded end 22.

Referring to FIG. 4, as the furnace (not shown) represented by framework 4 tilts, the operator 18 remains in a vertical plane. As the furnace tilts toward the tap side or the slag side, limit switch 1 rotates around the operator shaft 14 on the pillow blocks 10 and 11. As the fumace and limit switch oscillate large bevel gear 15 remains stationary. However, by virtue of weight 19 sufficient torque is transmitted to large bevel gear 15 to rotate small bevel gear 9. This smaller gear 9 is keyed to limit switch shaft 5 thereby rotating this shaft and the cams (not shown) with the limit switch and activating the electrical contacts (not shown) also contained within the limit switch.

An operator according to the present invention would be used in the following manner. FIG. 1 depicts the oscillation of a tilting electric arc furnace of the Heroult type. The furnace can oscillate 40 towardthe tap side and 15 toward the slag side producing a total angle of rock of 55 Fastened to the furnace framework 4 is rotating cam limit switch I mounted on platform 2 and containing shaft 5. As shaft 5 rotates, cams (not shown) contained within said switch activate electrical contacts (not shown) thereby initiating various events.

Connected to shaft 5 is pinion 9 with a pitch diameter of 2 inches. Mounted on platform 2 are pillow blocks 10 and 11 which contain bores 12 and 13 of 0.885 inches. A 0.876inch diameter shaft 14 passes through said pillow block bores. Connected to shaft 14 is gear 15 with a pitch diameter of 4 inches in meshing engagement with pinion 9.

Fastened to shaft 14 and disposed intermediate pillow blocks 10 and 11 is 3-inch round bar 24. Vertically connected to round bar 24 is 2 foot 6%-inch rod 21 threaded at end 22. Attached to rod 21 is a 180 pound weight 19. Weight 19 is fastened at end 22 by nut 29.

The cams are calibrated by moving the furnace through the entire angle of rock. When a predetermined angle is reached a cam mounted to shaft 5 is adjusted. Whenever the furnace oscillation passes through this angle the rotating cam will activate this contact.

Referring to FIG. 1 a calibrated rotating cam limit switch using an operator of this invention would perform the following functions: Horizontal line CD represents a line drawn through the side of the furnace at floor level and line 0-0' represents a line drawn through the centerline of the furnace. Function a;

angle formed between furnace and line 0-0, 0, activating a signal indicating the furnace is level. Function b;

angle formed between furnace and line 0-0' on slag side, 5", whereupon a signal indicating furnace has slagged off is transmitted to the furnace computer for heat log print out. Function 0;

angle formed between furnace and line O-O' on tap side,

10, activating an emergency tilt signal indicating a malfunction during the refining period. Function d;

angle formed between furnace and line 0-0 on tap side,

10, whereby a DC operated furnace control circuit is activated. Function e;

angle formed between furnace and line 0-0 on tap side, l0, wherein fume duct relay is automatically activated when the furnace tilts 10 toward tap. Function f;

angle formed between furnace and line 0-0 on tap side, 30, whereby a signal indicating tap time is transmitted to the furnace computer for heat log print out. Function g;

angle formed between furnace and line 0-0' on tap side, 40, activating a signal that shuts off the hydraulic system thereby preventing further tilting of furnace.

We claim:

1. A limit switch operating structure for activating a rotating cam limit switch wherein said limit switch is adapted to oscillate with a tilting metallurgical furnace and said limit switch is provided with a horizontal shaft assembly containing a plurality of cams mounted thereon and a plurality of electrical contacts, said operating structure comprising:

a. a shaft about which said limit switch oscillates;

b. a first bevel gear connected to said switch shaft assembly;

c. a second bevel gear in meshing engagement with said first gear and connected to element (a); and

d. a pendulum assembly connected to element (a) and remaining essentially vertical as said limit switch oscillates so that said second bevel gear causes said first bevel gear to rotate said horizontal shaft assembly thereby activating said electrical contacts.

2. A limit switch operating structure as recited in claim 1 wherein element (a) is horizontal and perpendicular to said switch shaft.

3. A limit switch operating structure as recited in claim 2 wherein the ratio of the pitch diameter of said first bevel gear to said second bevel gear is 2: l.

4. A limit switch operating structure as recited in claim 3 wherein said element (d) further comprises:

i. a weight containing a central bore;

ii. a shaft containing a threaded end and passing through said central bore;

iii. means to fastensaid shaft to element (a); and

iv. means connected to said shaft threaded end to maintain said weight on said shaft.

5. A limit switch operating structure as recited in claim 4 wherein the oscillation of said limit switch is from about 0 to about 55. 

1. A limit switch operating structure for activating a rotating cam limit switch wherein said limit switch is adapted to oscillate with a tilting metallurgical furnace and said limit switch is provided with a horizontal shaft assembly containing a plurality of cams mounted thereon and a plurality of electrical contacts, said operating structure comprising: a. a shaft about which said limit switch oscillates; b. a first bevel gear connected to said switch shaft assembly; c. a second bevel gear in meshing engagement with said first gear and connected to element (a); and d. a pendulum assembly connected to element (a) and remaining essentially vertical as said limit switch oscillates so that said sEcond bevel gear causes said first bevel gear to rotate said horizontal shaft assembly thereby activating said electrical contacts.
 2. A limit switch operating structure as recited in claim 1 wherein element (a) is horizontal and perpendicular to said switch shaft.
 3. A limit switch operating structure as recited in claim 2 wherein the ratio of the pitch diameter of said first bevel gear to said second bevel gear is 2:1.
 4. A limit switch operating structure as recited in claim 3 wherein said element (d) further comprises: i. a weight containing a central bore; ii. a shaft containing a threaded end and passing through said central bore; iii. means to fasten said shaft to element (a); and iv. means connected to said shaft threaded end to maintain said weight on said shaft.
 5. A limit switch operating structure as recited in claim 4 wherein the oscillation of said limit switch is from about 0* to about 55*. 